Welcome to Texas, circa 2100, when severe drought and triple-dight temperatures — presently considered a heat wave — will become standard summer fare.

Wait, there's more. Rising seas will increase the inland reach of hurricane storm surges and threaten low-lying coastal areas. Rainfall may remain the same, but will come in shorter bursts, leading to more flooding. Warmer temperatures will cause rivers traversing Central and South Texas to run dry before reaching the coast.

Such is a probable climatic future for Texas and the Gulf Coast if a global warming report released Friday in Paris proves accurate.

The Intergovernmental Panel on Climate Change report, six years in the making, concludes that the average global temperature should increase between 3.2 and 7.1 degrees Fahrenheit in the next century. And the seas should rise between 7 and 23 inches because warm water expands, and some glaciers are melting.

Most scientists praised the report, although some, such as NASA's Jim Hansen, said it underplayed the overall risk. A few others, and a number of think tanks, panned it for exaggerating the risk. They cast doubt on the conclusion that humans, through fossil-fuel burning and other greenhouse gas-emitting activities, are primarily driving global temperatures upward.

Imperfect science

Assuming the report — a rigorous scientific "best guess" of what lies ahead unless greenhouse gas emissions are soon dramatically cut — is correct, what does it mean for Texas?

The IPCC projections are based upon increasingly sophisticated models that compute an average global temperature.

However, even the model makers admit they are not perfect and do not capture every nuance of atmospheric physics. Regional modeling remains even more an imperfect science.

That lack of precision explains the broad leeway in future temperature projections.

Katharine Hayhoe, a Texas Tech University geoscientist, has employed statistical methods to predict what the weather will be like in Texas if the IPCC projections were to come true for the globe.

Her predictions for summer temperatures, if the world continues to rely on fossil fuels to meet its energy needs, call for winter temperatures to climb by 5 to 9 degrees by the year 2100, with summer temperatures going up as much as 7 to 15 degrees.

The state climatologist, John Nielsen-Gammon, said he didn't expect summer temperatures to rise by 15 degrees. He noted that the greatest warming is expected at the poles.

Indeed, during the past century, Texas has lagged a bit behind the warming Earth. The state's average annual temperature, from 1900 to 1970, actually declined from just above to just below 65 degrees.

Since about 1970, however, the state's average temperature has begun inching up about half a degree per decade.

"The overall trend is definitely smaller in Texas, which is to be expected because we're closer to the equator," said Nielsen-Gammon, a professor of meteorology at Texas A&M University.

Paradoxical prediction

It shouldn't take more than a few degrees to disrupt Texas — bringing more heat waves, flooding and, paradoxically, drought, local scientists say.

"Texas will face a number of challenges, but the most serious is probably a shortage of water," said Gerald North, distinguished professor of climate at Texas A&M University.

Water evaporates quicker at higher temperatures. Although North said model results vary, Texas generally is expected to get a bit less rainfall. To offset the increased evaporation in a warmer Texas, the state would need 25 percent to 40 percent more rain, he said.

The result could be desertifi-cation of the western half of Texas. Currently, Austin gets about 2.6 inches of rain per month. If temperatures climb

5 degrees, and there's no additional rainfall, evaporation effectively would cut the monthly total to 1.6 inches, North said.

Rivers may run dry

Rivers — such as the Brazos, Colorado and Rio Grande — that are sustained by runoff probably would dry up before reaching the Texas coast, he added.

"We are changing the composition of the atmosphere in a way that will promote warming, in a way that will have consequences," Barron said.

"I don't think you can argue about that any more. You just can't."

Fewer water resources would harm Texas' farming industry, said Bruce McCarl, a professor of agricultural economics at A&M. Based upon the IPCC global warming scenarios, he said, Texas could lose 40 percent of its crop acreage.

In warmer weather, crops require more water, and a drier Texas bodes poorly for universal access to irrigation, upon which much of the state is dependent. Corn, rice and grazing livestock would be vulnerable, he said, but some crops, such as tomatoes, citrus fruit and cotton, could benefit from the heat.

Many models suggest an even slightly warmer world will significantly increase the number of heat waves, which often come when high-pressure systems dominate the atmosphere. Under such conditions temperatures rise and winds fall.

These changes won't come immediately, the scientists say. Climate change generally is a gradual process rather than one of singular catastrophes. Humans are slowly, and perhaps somewhat irreversibly changing their world, they contend, and not for the better.

"If you're worried about the weather over the next five to 10 years, nothing alarming should happen," Nielsen-Gammon said. "But if you care about the globe 100 years from now, there are lots of reasons to be alarmed."